Tailgating (also known as piggybacking) is a significant problem in a wide variety of security and access control applications. Tailgating or piggybacking is the entry into or out of a controlled area or through a controlled access portal of more persons, objects or vehicles than are allowed by access control rules. For example, a tailgating event occurs when persons, generally on foot or in a vehicle, attempt to gain access to an area for which they do not have the required credentials. Another example of tailgating occurs when an unauthorized person on foot or in a vehicle attempts to follow a person (again on foot or in a vehicle) with proper access credentials into a controlled access area. A variation on this approach is for the unauthorized person on foot or in a vehicle to attempt to enter the controlled access area when an authorized person (in a vehicle or on foot) leaves the area.
Another example of tailgating (or piggybacking) is where a person sits on the shoulders of another person or is carried in some other way by the other person into the controlled access area. In all of the foregoing, the participation of the authorized individual may be inadvertent, voluntary, or coerced. In the remainder of this document, these cases and other similar cases are referred to as tailgating.
A related problem arises where someone attempts to enter on foot or in a vehicle through an “exit only” access point. This unauthorized use of an exit portal can be referred to as reverse entry. This access control violation arises, for example, when a person attempts to gain access to a controlled area using the exit of a one-way elevator (an elevator intended to be accessible only from inside the controlled area), escalators (by running the wrong direction), one-way revolving doors, or an exit passage. Alternatively, persons on foot may attempt to enter a controlled area by going over or under a gate at a vehicle-only entry or exit point. These methods and related events are collectively referred to herein as reverse entry.
The consequences of tailgating and reverse entry can vary widely. For example, the consequences may be purely economic as in the case of a successful perpetrator gaining access to an event venue, transportation or other such area without paying the admission or fare. Operators of entertainment venues, sporting facilities, parking facilities and transportation systems typically wish to prevent revenue loss from unauthorized entrants. In other cases, a successful perpetrator may steal something of value from the controlled area. Operators of industrial and manufacturing facilities, warehouse and other storage facilities, and housing areas, such as apartments or hotels, wish to prevent loss from theft. In yet other cases, a successful perpetrator may cause serious damage to property or harm to individuals in the controlled area. Airports, facilities handling hazardous materials, power plants and other utility facilities and large public places need to prevent the entry of persons wishing to cause property damage or harm to other people. To achieve these goals, it is necessary that doors, gates, passageways and other entry or exit areas be protected against unauthorized entry by perpetuators using tailgating and reverse entry methods.
Prior art access control systems have a long history starting with human guards and various types of mechanical locks. Modern access control systems use a wide variety of technologies and methods, including mechanical keypad or cipher locks, electronic keypad or cipher locks, contact-based or contactless smart cards or smart tokens (generally employing radio frequency or infrared communications), magnetic strip cards, and biometric control methods, such as retinal scans, fingerprint or handprint identification, facial feature identification, and voice print identification. Known access control methods do not prevent tailgating or reverse entry on their own. Moreover, human guards and persons authorized to access a controlled area may assist the perpetrators willingly or unwillingly, further complicating the situation.
Prior art approaches to the problems of detecting tailgating or reverse entry have not been successful. Most prior art approaches have applied either visible light or infrared break-beam technology. U.S. Pat. No. 3,727,034 to Pope, for example, discloses a system employing a pair of break-beams to determine the direction a person is traveling and count the number of people traveling through a passageway. U.S. Pat. No. 4,000,400 to Elder discloses a system applying a similar approach that also uses a pair of break-beams. These approaches suffer from a number of well-documented problems. If multiple people or vehicles pass the break-beam pair at the same time traveling in the same or opposite directions, the system cannot detect or resolve the ambiguity. People can crawl under or jump over a pair of break-beams. A person with another person on their shoulders or being carried in some other way is not detected. Since the break-beam requires a light source directly opposite the detector, the break-beam cannot be affected by the swing of a door. Architectural modifications may thus be required for installation. The above systems also disclose no provision for interfacing with external access control or other security systems. Further, the optical break-beams may not work in high ambient light conditions.
U.S. Pat. No. 5,519,784 to Vermeulen discloses a system that attempts to overcome some of the deficiencies of break-beam systems by employing an array of four or more sensors at floor level. However, this approach cannot detect cases where a person carrying another person on their shoulders or in some other way passes through the array. A four-legged animal passing through the array will likely trigger a false alarm. Architectural modifications may be required to force each person to pass through each beam. In addition, the system disclosed has no provision for interfacing with external access control or other security systems. Finally, as noted before, optical break-beams may not work in high ambient light conditions.
U.S. Pat. No. 4,303,851 to Mottier discloses a system using a pair of video cameras focused on two adjacent tracks through a flat mirror and connected to counter circuits. The tracks are perpendicular to a person's direction of travel. Persons passing through this array are detected and counted. While this approach removes some of the ambiguities associated with break-beam methods, problems still remain. A person with another person on their shoulders or being carried in some other way is not detected. The system disclosed has no provision for interfacing with external access control or other security systems. Further, architectural modifications may be required to keep all persons within the field of view of the cameras and to prevent the swing of a door from interfering with the field of view of the cameras.
U.S. Pat. No. 4,847,485 to Koelsch and U.S. Pat. No. 4,799,243 to Zepke disclose systems applying arrays of pyroelectric infrared sensors to directionally count people entering or leaving through a passage. The system in U.S. Pat. No. 4,799,243 employs a single linear array of sensors that may not detect a person with another person on their shoulders or being carried in some other way. Further, it is unclear whether several people entering or leaving in close physical proximity would be correctly detected. U.S. Pat. No. 4,847,485 attempts to overcome these deficiencies through the use of multiple sensor arrays. This approach has the drawback that it requires architectural modifications since each person must be forced to walk through all the arrays. The systems disclosed have no provision for interfacing with external access control or other security systems. Further, architectural modifications may be required since the swing of a door cannot affect the area monitored by the sensors. Both systems are also subject to environmental restrictions since they use pyroelectric sensors and are unsuitable for vehicle entrances.
U.S. Pat. No. 5,866,887 to Hashimoto et al. discloses a system that applies a similar approach but uses a moving sensor and pattern recognition to reduce both the cost and the ambiguity inherent in detecting multiple people at the same time. This system does not overcome all the aforementioned deficiencies, since the approach still relies on sensing biomass though detection of body heat of people.
U.S. Pat. No. 5,201,906 to Schwarz et al. discloses a system that applies a set of ultrasonic sensors in a revolving door structure. The sensors are interfaced to a local access control system to prevent or detect piggybacking. The ultrasonic sensors determine if more than one person is in one compartment or more than one compartment is occupied. This approach requires architectural modifications to most facilities, since a revolving door is required. The rate at which people can pass through the revolving door is likely less than a conventional door with security access. Further, this approach is unsuited for vehicle entrances.
U.S. Pat. No. 6,081,619 to Hashimoto et al. discloses a system that employs either linear or angular infrared distance or range-finding arrays. This approach has drawbacks in that some embodiments require architectural modifications since each person must be forced to walk through the array, and the observation area of the sensors cannot be affected by the swing of a door. The system disclosed has no provision for interfacing with external access control or other security systems. Finally, this system is subject to environmental restrictions since it uses infrared technology and is unsuitable for vehicle entrances.
The use of simple motion detection video is known in the security technology industry. Motion detection video uses frame-differencing and related methods applied to the output of a video camera. These methods suffer from problems such as changes in lighting and shadowing. Overlapping objects are often difficult to separate since there is no depth (three-dimensional) analysis and no attempt is made to analyze and track individual objects.
U.S. Pat. No. 5,581,625 to Connell discloses a system that uses a pair of stereoscopic video cameras and associated machine vision analysis to separate individual objects (e.g., people) in a line that partially overlap from the perspective of the stereo camera pair. This system makes no attempt to determine the motion of the people observed. Furthermore, there is no provision for interfacing the system with external access control or other security systems.